1. Field of the Invention
The present invention relates to a method and to an apparatus for evaluating the measured signals of a sensor, particularly for evaluating the signals of an inductive, measured-value sensor for marking the rotational position at an internal-combustion engine, whereby the sensor signal is supplied to an evaluation unit with which or in which, in particular, the appearances of zero axis crossings are identified.
2. Description of the Prior Art
Such methods and apparatus are known, in general, and, for example, enable the acquisition and processing of the signals of inductive, measured-value sensors as are utilized, for example, in internal-combustion engines in a great variety of arrangements as apparatus for marking rotational position. The magnetic flux generated by a power supply or by a permanent magnet that passes through an emitter coil is influenced, dependent on ferromagnetic material in the close proximity thereof, such that corresponding marks on a rotating disk that, for example, is secured to the crank shaft or the cam shaft, or acquired as flux maximum at pins or, respectively, as flux minimum at slots. This respectively corresponds to a zero-axis crossing of the induced emitter voltage with different tendency.
Standard embodiments, for example, are arrangement for marking the top dead center (TDC) with one or more pins or slots distributed over the circumference of the disk flywheel and with different angular positions relative to the physical TDC as well as, furthermore, arrangements for identifying, or, respectively, evaluating the angular velocity, whereby measurement is carried out at a gear rim, for example, at the starter gear rim of the disk flywheel and a TDC marking in the form of a defined gap may be additionally provided. A distinction must therefore be made between two instances. On the one hand, there are arrangements having a known polarity (pin or slot having emitters protected against pole reversal) or, respectively, having insignificant polarity (gear rim); by contrast thereto, arrangements of unknown, but significant polarity, are also to be covered, whereby an automatic pin/slot recognition is then desirable.
Depending on a number of parameters, such as emitter sensitivity, emitter spacing, geometrical execution of the marks, circumferential speed of the emitter disk, a very large range of voltages to be acquired usually results, typically, a usable range of the emitter voltage from 20 mV.sub.pp -100 V.sub.pp is required. In order to be able to process such a range of dynamics with the required accuracy in the acquisition of the zero-axis crossings, a gain control of the signal in the form of an AGC (automatic gain control) circuit or in digital form was heretofore employed in the known methods or, respectively, apparatus of the type generally set forth. This method, however, contains the disadvantages of a response phase as well as of a great expense in the control when high dependability is to be achieved over a great range of speeds given, at the same time, a great speed dynamic. Such conditions occur, for example, when transient motor conditions are to be acquired as represented, for example, by a dynamic power measurement (free, high acceleration vis-a-vis the inherent torque) or by the checking of the idling control (undershooting or, respectively, overshooting given abrupt load change). When relatively low speeds are then also to be simultaneously measured (for example, the starter speed given a compression measurement), then circuit designs realized with usually justifiable expense are usually overburdened.
In order to eliminate the speed dependency of the size of the useful signal, the German published application 32 34 383, for example, discloses a method and an operating device therefore, whereby markings of a rotating disk are evaluated with an inductive emitter such that the emitter signal is integrated and then supplied to a threshold switch. Although the disadvantage of the speed dependency of the size of the useful signal is therefore eliminated, the other influencing variables in this respect, such as emitter sensitivity, emitter spacing and geometrical execution of the marks are not. In addition, integrating systems having traditional emitter disks are sensitive to low-frequency disturbances having an inherently low level such as can occur, for example, as a consequence of a bearing play at starter speeds when the gyro-stabilizing forces are still too low.
Also, for example, the European patent documents EP 83 594 and EP 28 27 32 disclose methods and apparatus for generating speed-dependent signal sequences from the signals of inductive emitters whose shared feature, however, is that it is not the signal zero-axis crossing that is interpreted, but that an optimally-accurate triggering should occur at a defined signal quantity. Since, by definition of the zero-axis crossing of the reference quantity must be utilized for certain measurements at, for example, internal-combustion engines, for example for calculating the start of delivery angle at a diesel motor, a utilization of this method is not suitable for all signals of inductive emitters employed in the diagnosis of internal-combustion engines. In addition, the follow up of the trigger level by peak value measuring devices having a defined discharge time constant can only represent a compromise when broadbands of speed are to be processed given high motor dynamics since the inaccuracies thereby made directly enter into the trigger time.